I recently decided that enough was enough -- I was going to learn to use grep fluently. It's been all of three hours and I'm already stumped by this toy problem.

I'm currently syncing a RAID5 array, the progress of which can be monitored by reading /proc/mdstat. The output of cat /proc/mdstat is shown below.

$ cat /proc/mdstat

Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] 

md1 : active raid5 sda4[0] sdb4[1] sdc4[2]

      5858765824 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/3] [UUU]

      [=============>.......]  resync = 67.3% (1972073120/2929382912) finish=205.7min speed=77537K/sec



md0 : active raid5 sda3[0] sdb3[1] sdc3[2]

      998400 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/3] [UUU]



unused devices: <none>

For fun, I thought I would use watch to monitor /proc/mdstat in real time, pipe it's output into grep, and show only the estimated remaining time.

My approach is as follows:

watch cat /proc/mdstat | grep finish=d+.d | grep d+.d

I'm stumped as to why this produced no output. In fact, the first grep expression produces no output, even though it seems to work on Regex101.

What am I doing wrong?